Method and apparatus for formulating microspheres and microcapsules

ABSTRACT

A process and apparatus for making and formulating microcapsules and microspheres which can easily be maintained aseptic throughout all stages of the production process.

BACKGROUND OF THE INVENTION

Microcapsules and Microspheres formed from various natural and syntheticpolymers and resins have become popular delivery vehicles for variousactive agents such as drugs, diagnostic reagents and the like.Degradable microcapsules and microspheres are of particular interest foruse in so called “depot” formulations, where delivery of the activeagent over an extended period of time is desired. Despite the growingnumber of uses of microcapsules and microspheres, there remains a needfor an economic, safe and reliable method for their manufacture andformulation that avoids the most significant wastes and expensesassociated with existing methods, while simultaneously enabling theability to aseptically formulate the products in a simple and efficientmanner.

Processes for preparing microcapsules and microspheres typically involvethe formation of at least one dispersed phase in a continuous phase. Thedispersed phase typically includes the active agent. In the case ofmicrospheres, the dispersed phase will also typically include polymer sothat, upon solidification in the continuous phase, the dispersed phasebecomes a microsphere. Microcapsules are similarly formed using multiplephases. In a typical practice, a water-oil-water (w/o/w) emulsion isformed, and the polymer caused to precipitate out of one phase onto thesurface of a dispersed phase to form a capsule wall thereon uponsolidification of the polymer. Once the capsules or spheres areproduced, they must then be formulated into a finished dosage form.

Most microsphere processes result in a suspension of particles in asuspending liquid that is not the suspending liquid desired for thefinal dosage form. Current techniques for processing and formulatingmicrospheres and microcapsules into the final dosage form typicallyinvolve dead end filtration and powder filling processes. Although thepowder processes can be made aseptic, they tend to have the drawbacks ofusing large volumes of flammable solvents, capital intensive equipmenttrains are generally required for a fixed scale and they take acomparatively long time to produce a finished batch. Likewise, the timeand capital expense associated with powder filling processes can put oneat a significant competitive disadvantage.

There is a need for a process that can efficiently, economically andaseptically process and formulate microcapsules and microspheres intofinal dosage forms.

DISCLOSURE OF THE INVENTION

The present invention is directed to a method and apparatus forprocessing and formulating active agent containing polymer bodies, andmore particularly microspheres and microcapsules. The method andapparatus according to the invention are ideal for formulatingmicrocapsules and microspheres suitable for carrying drugs, diagnosticreagents, or various other active agents into final dosage form. Theinventive method provides a simple, economic, efficient and asepticmeans of formulating a product wherein the sterile field need not becompromised throughout the entire production cycle. As used herein,terms such as “sterile” and “aseptic” are taken to mean sterile oraseptic enough to meet current USP standards. The apparatus according tothe invention is relatively inexpensive and easily broken down andsterilized, thereby significantly reducing capital expendituresassociated with aseptic powder processes. Moreover, product batches canbe produced with shorter cycle times than current processes bacth ofleuprolide containing microspheres can be prepared and processed intofinal dosage vials on the order of three days.

The method and apparatus of the invention are most preferably employedto formulate microspheres produced in accordance with the processdisclosed in co-pending application Ser. No. 08/800,924, filed Feb. 13,1997 U.S. Pat. No. 5,945,126, incorporated herein by reference.Preferably, the active agent is a drug or diagnostic agent and themicrospheres are intended for the delivery of such drug or diagnosticagent to a patient in need thereof. The preferred drugs may be peptidedrugs, proteinaceous drugs, steroidal drugs, non-steroidal drugs, simplecompounds and so on. A representative list of suitable drugs and otheractive agents may be found in U.S. Pat. Nos. 5,407,609, 4,767,628,3,773,919 and 3,755,558, all incorporated herein by reference. Ofparticular interest are LH-RH agonists such as leuprolide, triptorelin,goserelin, nafarelin, historelin and buserelin, LH-RH antagonists,somatostatin and its analogs such as octreotide, human, salmon and eelcalcitonin, growth hormones, growth hormone releasing hormones, growthhormone releasing peptide, parathyroid hormones and related peptides,interferon, erythropoietin, GM-CSF, G-CSF, thymosin, antitrypsin,enterostatin, and chemotherapy drugs, antibiotics and analgesics forregional administration. An especially preferred drug for use in theinstant invention is leuprolide.

The advantages of the invention are accomplished by maintaining andprocessing the microspheres or microcapsules as a suspension. Whilesignificant advantages can be achieved by processing the product as asuspension, there is also a significant potential for product losses ifadequate precautions are not taken to maintain the suspension and ensureproper product flow throughout the process.

Generally speaking, the formulating process of the invention involvesthe concentration, washing and formulating of agent containing polymerbodies, i.e., microspheres or microcapsules, that are maintained in asuspension of a continuous phase. Typically, the continuous phasecontaining the polymer bodies is initially water, or water containingresidual impurities from the process used to make the microspheres ormicrocapsules, such as surfactants, residual solvent and the like. Inorder to formulate the polymer bodies into a final product it isnecessary to process the polymer bodies into an appropriate sterileconcentration of polymer bodies in a suitable pharmaceuticallyacceptable diluent or carrier, i.e., formulating medium. The presentprocess accomplishes this aseptically by processing the polymer bodiesas a suspension using a filter capable of removing the continuous phasewithout deleteriously effecting the suspension of polymer bodies. Thecontinuous phase which, as noted, can initially be water, butsubsequently during the process can be other suspending media, includingwater for injection and formulating medium, is then cycled back to aprocess vessel as a suspension for further processing in subsequentphases. Advantageously, a hollow fiber filter provides an ideal means ofaccomplishing the concentration of the polymer bodies, and thereplacement of the continuous phase with other continuous phases such aswater and/or formulating medium.

In practicing the inventive method of formulating according to theinvention, a suspension of agent containing polymer bodies in acontinuous phase is provided in a process vessel. In a preferredembodiment the apparatus will employ only a single processing vessel,which serves to formulate the microspheres and microcapsules inaccordance with the method described herein. However, configurations canbe devised in which the process vessel performs multiple functions. Forexample, it can also serve as a solvent removal vessel as a preliminarystep to the practice of the inventive method. Similarly, multipleprocess vessels can be employed in series, each functioning to performone or more phases of the formulating process, such as a concentratingphase, a washing phase and a formulating phase, respectively.

Since one of the advantages of the invention is derived from thesimplicity and limited capital costs of the apparatus used, it isgenerally preferred that a minimum number of vessels be employed.However, on larger scale processes, where significant volumes are to beprocessed, it may be necessary to employ two process vessels and hollowfiber filters in series to minimize losses. Thus, in another preferredembodiment, the first process vessel serves as a solvent removal vessel,into which a relatively large volume of formed or forming microspheresare directly transferred from a means for forming them, such as anin-line mixer, and also serves to perform a concentrating and washingphase. In order to minimize losses, a second process vessel and hollowfiber filter are employed to further reduce the volume and increaseconcentration, and also to perform the formulating phase.

While maintaining said polymer bodies in suspension in the processvessel, such as by magnetic stirrer, impeller, recirculation apparatusand the like, the continuous phase is replaced with a formulating mediumby moving the suspension through the filter apparatus. Preferably, thesuspension is circulated through the filter and back to the processingvessel, rather than to down stream vessels. Conceptually, any filterthat is adapted to eliminate continuous phase and return the polymerbodies as a suspension to a process vessel will suffice for the practiceof the invention, with the noted hollow fiber filter being preferred. Asnoted, the continuous phase will typically initially be water containingnot only the polymer bodies, but also various impurities from themicrosphere/microcapsule preparation process. Thus, while, dependingupon the nature of the active agent and end use to which the productwill be put it is possible to replace the initial continuous phasedirectly with formulating medium, the process according to the inventionwill preferably include a washing phase. Likewise, since theconcentration of polymer bodies in the initial continuous phase willgenerally be significantly less than the concentration required for thefinal product, the process will also preferably include a concentratingphase, in which the suspension is run through the filter to eliminatecontinuous phase. Once the suitable concentration of polymer bodies inthe formulating medium is obtained, as ascertained by sampling andassaying the suspension from the processing vessel, the suspension ofagent containing polymer bodies and formulating medium is removed fromthe process vessel for subsequent processing, such as filling into finalproduct vessels.

The invention is also embodied in a novel and advantageous apparatus forformulating the agent containing polymer bodies. In particular, theapparatus employs a process vessel that is adapted to maintain asuspension of polymer bodies in a continuous phase that is coupled tothe noted filter in a manner that enables the suspension to be processedthrough the filter so as to eliminate continuous phase, and thereafterreturn the suspension to the process vessel, or one or more additionalprocess vessels, for further processing. To accomplish the furtherprocessing, the apparatus includes a source of formulating medium and,when a washing phase is employed, as source of wash water. The inventiveapparatus thereby enables the microspheres or microcapsules to beprocessed as a suspension. Advantageously, the apparatus is relativelysimple and inexpensive, and highly conducive to processing the polymerbodies aseptically.

As will be apparent, in its simplest configuration the apparatus willemploy a single process vessel and filter combination that is coupled toa source of microspheres or microcapsules, as well as the water sourceand formulating medium source. However, it is likewise possible for aplurality of filters and process vessels to be coupled in series, sothat the output from a first processing vessel and filter can betransferred to a second process vessel and filter for, e.g., a washingstep, which output may then be transferred to yet a third process vesseland filter for substitution of water from the washing step withformulating medium. Likewise, the separate vessels could all utilize thesame filter. Other configurations will also be apparent to those ofordinary skill in the art in view of the instant disclosure.

As noted, many of the advantages of the present invention are derivedfrom the ability of the apparatus to process the microspheres as asuspension. Thus, the preferred apparatus of the invention is configuredusing simple elastomeric tubing, peristaltic pumps and pinch clamps orsimilar devices. Such components not only advantageously add to the lowcosts associated with the invention, they enable the maintenance of thesuspension by eliminating settling points and other areas wherepotentially significant losses can occur, such as mechanical valves,sharp turns, elbows and the like. The various components of the systemare thus coupled in a manner that maximizes the ability of the system tomaintain the polymer bodies in suspension. It is to be understood thatthe term “coupled” as used herein means that the various components areoperatively coupled so that the contents of one element can move toanother element, but can include intermediate elements and components.

In another aspect of the invention there is provided a method of makingand formulating agent containing polymer bodies. The polymer bodies areformed by forming a dispersed phase comprising an active agent, andproviding a continuous phase in which the dispersed phase will form anemulsion, at least one of the dispersed and continuous phases comprisingpolymer. The dispersed and continuous phases are introduced into areactor vessel that includes means for forming an emulsion, and anemulsion of the dispersed phase in the continuous phase is formedcausing the polymer to form microspheres or microcapsules containing theactive agent. Likewise, a series of reactors may be used to form adouble emulsion for forming microcapsules. Thereafter, the said emulsionis transported from the reactor vessel to a solvent removal vessel andsolvent is removed therein. Once the desired level of solvent removal isobtained, the polymer bodies are formulated by maintaining them insuspension in accordance with the aforementioned formulating process. Ina preferred embodiment, the means for forming an emulsion is an in-linemixer. In another aspect of the invention, the means for forming anemulsion is a static mixer.

Many additional features, advantages and a fuller understanding of theinvention will be had from the following detailed description of thepreferred embodiments and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stylized schematic flow diagram of the formulating processaccording to the invention.

FIG. 2 is a stylized representation of an apparatus useful in carryingout the formulating process according to the invention.

FIG. 3 is a stylized representation of a filter apparatus according tothe invention.

FIG. 4 is a stylized representation of another apparatus according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally to FIG. 1, the formulating process of the inventioncan be described. Represented generally at 10 is a source ofmicrospheres or microcapsules. As noted, the microspheres ormicrocapsules can be prepared by any means known in the art such asthermal processes, single and double emulsion processes and the like asset forth in, for example, U.S. Pat. Nos. 4,675,189, 5,534,269,3,773,919, 5,611,971 and 4,767,628, incorporated herein by reference,static mixing processes as disclosed in Published International PatentApplication No. WP 95/13799, incorporated herein by reference, by highintensity in-line continuous processing as set forth in co-pendingapplication Ser. No. 08/800,924 U.S. Pat. No. 5,945,126, incorporatedherein by reference, and solution based processes such as disclosed inU.S. Pat. Nos. 5,407,609, 4,818,542 and 4,389,330, incorporated hereinby reference. Preferably, source 10 is an in-line mixer for providingmicrospheres in accordance with the method disclosed in copendingapplication Ser. No. 08/800,924 filed Feb. 13, 1997. Now U.S. Pat. No.5,945,126.

The microspheres or microcapsules may be transferred from source 10 to aholding tank 24 via harvest line 14. Although in the preferredembodiment a suspension of solidified dispersed phase particlessuspended in the continuous phase will generally be transferred to tank24, depending upon the specific nature of the process for making themicrospheres or microcapsules, the polymer bodies being transferred tothe tank 24 may not yet be solidified or otherwise may still be in theprocess of forming. Transfer to the holding tank, in the case of thepreferred in-line continuous process, can be accomplished by the pumpingaction of the in-line mixer itself, or otherwise by vacuum or pumpaction as would be apparent to those of ordinary skill in the art inview of the present disclosure. In another embodiment, the polymerbodies may be transfered to a process vessel that will serve as asolvent removal vessel as well as perform one or more of theconcentrating, washing and formulating steps.

Once an adequate volume of continuous phase containing the polymerbodies has been provided in holding tank 24, the formulating processaccording to the invention can commence. The particular volumeintroduced into tank 24 will vary depending upon the size of theparticular apparatus employed and is essentially arbitrary as long asthe material can act as a fluid and be maintained in suspension asneeded. Typically, the initial volume present in a solvent evaporationtank, or in holding tank 24 will be significantly greater than thatbeing processed in formulating vessel 16, perhaps on the order of fortyliters versus one to three liters. Likewise, the concentration ofmicrospheres or microcapsules will be significantly more dilute thanthat required in the final formulation. Unlike open and dead endfiltration systems, a significant advantage of the present invention isthe ability to concentrate a large volume of dilute continuous phaseinto a small volume of concentrated continuous phase in a closed systemin a fast, efficient and aseptic manner.

As seen in FIG. 1, formulating vessel 16 is coupled to a water forinjection (WFI) source 18, a formulating medium source 20 and a hollowfiber filter 22. It is important in the practice of the preferredembodiment, where the advantages of a generally continuous process areto be obtained, to coordinate and control flow of material into and outof the formulating vessel 16. In this way suitable amounts of continuousphase containing agent containing polymer bodies, WFI and formulatingmedium can be selectively metered into formulation vessel 16 atappropriate rates and in appropriate amounts while keeping the volume inthe formulating vessel 16 approximately constant.

As noted, because of the potential for significant losses it isimportant to maintain the polymer bodies in suspension. settling of thepolymer bodies leads to potentially significant losses, as well asclogging in the various lines and orifices. By maintaining the polymerbodies in a suspension, the advantageous method and apparatus of theinvention are made possible. Thus, holding vessel 24 will include meansfor maintaining the polymer bodies in suspension, such as a magneticstirrer in the case of smaller scale apparatus, or an impeller,recirculation apparatus or the like. Likewise, as seen in FIG. 2,holding tank 24, WFI source 18 and formulating medium source 20 arecoupled to the formulation vessel 16 via elastomeric tubing lines 124,118 and 120 respectively. Each line may be selectively closed fromaccess to vessel 16 via suitable clamps, shown generally at 28. In thisway, the use of valves or similar mechanisms for selectively controllingthe flow of polymer body suspension to the formulation vessel that canpotentially cause significant losses are avoided. The polymer bodysuspension, WFI and formulating medium are selectively pumped toformulating vessel 16 via peristaltic pump 30 and tubing line 130 which,again, helps to prevent losses. Other pumping apparatus suitable for usein the present invention may include rotary lobe pumps and centrifugalpumps. The principal consideration is the ability of the tubes, pumpsand connections used in the present apparatus to facilitate themaintenance of the suspension and to eliminate or minimize lossesthrough settling. Other means of maintaining the suspension andminimizing losses would be apparent to those of ordinary skill in theart in view of the instant disclosure.

As shown, formulating vessel 16 includes a plurality of ports for theintroduction and removal of continuous phase containing polymer bodiesto and from the vessel. Likewise, as will be apparent, the vessel 16includes means for maintaining the polymer bodies in suspension therein(not shown). Suitable means may vary depending upon the scale of theapparatus, and will be apparent to those of ordinary skill in the art inview of this disclosure. Such means can include magnetic stirrers,impellers, recirculation devices and the like.

In the practice of the invention a suspension of polymer bodies, i.e.,microspheres or microcapsules, in continuous phase is pumped intoformulation vessel 16 via pump and tube 124. A suitable volume ofsuspension will vary depending upon the scale of the process. Volumesranging from about 1 to 40 liters may be employed depending upon thescale of the apparatus. In the preferred process of formulating LH-RHagonist containing microspheres, a suitable starting volume for theapparatus employed is on the order of about 1 to 3 liters. Generally,the concentration of polymer bodies in the continuous phase that isintroduced into the formulating vessel will not correspond to theconcentration required for the final product. For example, the holdingtank may contain on the order of 40 liters of continuous phase having amicrosphere concentration on the order of about 2 to 3 grams per liter.Thus, while maintaining the polymer bodies in suspension in formulationvessel 16, the suspension undergoes a concentration phase.

During the concentration phase the suspension is pumped from theformulation vessel 16 via peristaltic tubing 122 to hollow fiber filter22. As the suspension passes through hollow fiber filter 22 continuousphase is removed by the filter, thereby concentrating the suspension ofpolymer bodies in the continuous phase. As shown, waste continuousphase, or permeate, removed by filter 22 is transferred to waste tank 32via line 132 and pump 50. A pump is not required, but may be useful tocontrol the rate of removal. After the suspension passes through thefilter 22 it is transferred back to formulation vessel 16 viaelastomeric tubing 222. The use of elastomeric tubing, such as silastictubing, and peristaltic pumps advantageously enables the processing ofthe suspension according to the invention with a minimum of losses. Withthe apparatus currently employed, about 40 L of continuous phase fromtank 24 is pumped into formulating vessel 16 at a rate of about 400ml/min. This corresponds the rate at which the filter 22 removescontinuous phase in the form of permeate. The continuous phase iscontinually pumped in and taken out at a rate of about 400 ml/min. untilall of the continuous phase has been transferred from tank 24 and thevolume in the formulating vessel 16 is on the order of 1-3 liters. Incarrying out the process, the rate at which the continuous phase ispumped through the filter 22 via tubing 122 and 222 is also important.With the preferred filter, the rate at which continuous phase is removedby the filter should not exceed about one third of the flow rate ofcontinuous phase through the filter, otherwise flow and cloggingproblems can occur. Thus, with the preferred filter removing 400 ml/minthe flow rate through the filter should be on the order of about 2liters/min.

The preferred configuration of hollow fiber filter 22 is seen best inFIG. 3. As shown, filter 22 is coupled via peristaltic tubing 122 and222. In this way, no sharp turns or 90 degree elbows are present as asignificant source of losses. The preferred filter 22 is the CFP-A-E-6A,0.45 micron hollow fiber filter from A/G Technology, supported on aflexstand in the example. In the practice of the preferred embodimentthe filter configuration has been modified to employ connections 34 inorder to eliminate settling points, which would otherwise result insignificant losses. For the scale of apparatus represented this filterserves to eliminate about 400 ml of continuous phase per minute. Itemploys a 1 mm diameter fiber, although fiber diameter and other filterparameters will vary depending upon particle size, the nature of theformulating medium and the like. Selection of suitable filter units willbe apparent to those of ordinary skill in the art in view of the instantdisclosure. For a typical pharmaceutical product, polymer bodyconcentrations on the order of 40 to 200 grams per liter will berequired. In the case of the preferred LH-RH agonist containingmicrospheres, a target concentration of from about 27 mg/ml to about 150mg/ml is desired depending upon the final dosage form. In practice, itis desirable to aim for a suspension that is slightly more concentratedthan required for the final product because a dilution correction tofinal dosage concentration is typically a simpler procedure than aconcentrating correction. Given the volume of permeate generated by theparticular filter and pump used, and the flow rate of continuous phasethrough the filter, one can readily approximate the time necessary toobtain the desired concentration or, in the case of the washing andformulating phases, the approximate time necessary to replace onecontinuous phase with another. Verification is then readily ascertainedby monitoring the weight of permeate.

Once the suspension of polymer bodies in the formulation vessel has beenconcentrated to the approximate concentration of microspheres ormicrocapsules necessary in the final product, clamp 28 b on tubing 118is removed to allow water for injection to be introduced into vessel 16from WFI source 18 to commence a washing phase. In the washing phase thepolymer bodies are maintained in suspension in vessel 16 and thesuspension pumped to filter 22 via tubing 122. In the preferredembodiment, the volume in the formulating vessel 16 is maintained atabout 1-2 liters by coordinating the pumps 30 and 50 so that the flowrates of water in from source 18 and continuous phase permeate outthrough line 132 are matched at 400 ml/min. As noted, with the filterremoving approximately 400 ml/min., and the flow rate in loop 122/22/222maintained at about 2 l/min., the time required to replace the volume ofcontinuous phase with an equal volume of water for injection can bereadily determined. In the preferred embodiment, additional passes aremade to ensure a complete washing.

Once the washing phase is complete the formulating phase is commenced.The WFI source 18 is closed and the formulating source 20 opened byselectively clamping and unclamping the appropriate clamps 28 b and 28c. Formulating medium is thus pumped into formulating vessel 16 via pump30 and tubing 120 and 130. As with the washing phase, the pumps 30 and50 are coordinated to maintain the volume in the formulating vessel andthe process of passing the suspension of polymer bodies through filter22 commences. The polymer bodies are maintained in suspension in vessel16 and the suspension pumped to filter 22 via tubing 122 until the WFIis replaced with formulating medium. To ensure complete formulation, thepreferred embodiment passes the suspension through filter 22 in excessof the theoretical time necessary to replace the volume in the vessel16.

Once formulated, the composition may be assayed for determination ofdrug content of the suspension to determine the final required dosage.As would be apparent to those of ordinary skill in the art in view ofthis disclosure, final dosage adjustment is determined by sampling andassaying the suspension and performing a concentrating or dilutingcorrection as needed.

Once the desired concentration of polymer bodies in the formulatingmedium is obtained, the volume of formulated composition from vessel 16may be removed and transferred for subsequent processing into finalproduct. In the preferred process the formulated composition istransferred from vessel 16 to an aseptic filling machine where theproduct is filled into product vials or other suitable containers. Thisis done aseptically by disconnecting tubing 122 and connecting transfertubing 35 which couples to 29 a of vessel 16 to the filling station, allthe while maintaining the composition sterile and in suspension.

It will be apparent that irrespective of the particular method of makingthe microspheres or microcapsules, solvent removal is generallyimportant, especially when the resulting microspheres are intended forclinical applications. However, in some instances it may be possible tobypass the solvent evaporation tank and transfer the microspheres ormicrocapsules directly to the formulating vessel 16. Likewise, it mayalso be desirable for formulating vessel 16 to serve both as theformulating vessel and as the solvent evaporation tank.

The process according to the invention will now be exemplified by thefollowing non-limiting example and with reference to the accompanyingdrawings.

EXAMPLE

Initially, a suspension of microspheres of leuprolide acetate preparedby the process according to the aforementioned co-pending applicationPat. No. 08/800,924 filed Feb. 13, 1997 U.S. Pat. No. 5,945,126, istransferred through a wet sieve into the holding tank from a solventevaporation tank (not shown). When all of the suspension, in thisexample approximately 40 liters, is transferred to the holding tank 24,the pump is stopped and the formulating process begins. Theconcentration phase is commenced by moving the suspension through thehollow fiber filter, A/G Technologies CFP-A-E-6A, 0.45 micron, supportedon a Flexstand.

Approximately 1.2 L of suspension is moved into the process vessel usingperistaltic pump 30 and the suspension maintained in the process vesselby magnetic stirrer. Peristaltic pump 40 is started to circulate thesuspension through the hollow fiber filter at a rate of about 1.75L/min. Peristaltic pump 50 on the filter outlet is adjusted to obtain apermeate flow from the filter to the waste tank of about 400 ml/min. Theflow rate of peristaltic pumps 30 and 50 are matched to maintain fromabout 1000 ml to 1300 ml of the suspension in the formulating vessel.The circulation of the suspension through the hollow fiber filter unitis maintained by peristaltic pump 40 and continued until approximatelyall 40 liters of the suspension is transferred from the holding tank 24to the formulating vessel 16. The permeate flow from the filter isreduced to approximately 300 ml/min to achieve more circulation of theretained suspension (retentate) through the filter and prevent themicrospheres from settling in the circulation path. This also helpsreduce microsphere or microcapsule adherence to the wall of the filter.After approximately 90 minutes, the concentration phase was complete.The volume in vessel 16 at the end of the concentration phase was 1.10L, and the weight of permeate was 36.25 Kg.

To commence the washing phase clamp 28 a is closed and clamp 28 b openedto permit water from the WFI vessel to enter the formulating vessel 16via pump 30. Approximately 1.2 L of suspension is maintained in theformulating vessel by adjusting peristaltic pump 30. The suspension ofWFI and polymer bodies is circulated through the hollow fiber filteruntil approximately 10 kg of WFI is mixed with the suspension. This isdetermined by measuring the weight of the permeate waste vessel. In thisexample, washing was complete after about 20 minutes and the weight ofpermeate was 9.96 kg.

The formulating phase is commenced to exchange the formulating diluentor medium for the WFI. Clamp 28 b is closed and clamp 28 c opened. Thecirculation rate through the hollow fiber filter is maintained atapproximately 2 L/min. and the permeate flow rate is maintained atapproximately 300 ml/min. Circulation of the formulating medium andpolymer bodies through the filter is continued until about 10 L (i.e.,10 kg) of the formulating medium has been processed. As with theprevious step, this may be determined by monitoring the weight of thepermeate waste tank. In this example, the starting weight of thepermeate waste was 10 kg and the final weight 20.06 kg, with theformulating step thus being completed after about 30 minutes.

To ensure final product specifications, it is necessary to sample andfine tune the polymer body concentration depending upon the finaldesired dosage, which in turn depends upon the particular drug andpolymer body morphology employed. This is accomplished by determiningthe volume of the suspension in the formulating vessel and reducing itto 700 ml. Once this volume is obtained, pump 50 is stopped. Thedirection of pump flow on pump 40 is then quickly changed to draw thesuspension from the hollow fiber filter into the formulating vessel.When air bubbles start coming through the dip tube of the formulatingvessel the pump is stopped and clamps 29 a, b and c are closed. Quickconnects 33 a, b and c are disconnected and the junctions wrapped withsterile foil. While the mixing rate is maintained in formulating vesselthe suspension is sampled.

Four 4×5 cc sample vials were labeled A, B, C and D. Using an 18 gauge9″ needle with stopcock through the septum on the vessel 16approximately 2 ml of the suspension was drawn into a syringe. Thesyringe was disconnected from the needle and the 2 ml transferred intovial A. This procedure was repeated with the remaining vials whileinsuring that the needle remained in the septum of the suspensionvessel. The vials were tare weighed. The suspension in vials A, B, C andD weighed 2.17 g, 2.01 g, 2.19 g, and 2.75 g, respectively. The sampleswere then tested for drug content and the suspension in the processvessel maintained by mixing until the results obtained. Once the resultsare obtained, stirring was stopped and the formulating vessel wasquickly moved to a balance and the weight of the suspension thereindetermined to be 1173 g. For this drug if assay value is less than 7.5mg/g, then a concentrating adjustment must be made. If the assay valueis greater than 7.5 mg/g, then a diluting correction must be made. Theassay in this example indicated that the drug content of leuprolideacetate was 9.6 mg/g, thereby requiring a dilution correction. Bymultiplying by the weight of the suspension and calculating the weightof suspension necessary to obtain 7.5 mg/g of leuprolide acetate it wasdetermined that an additional 328 g formulating medium needed to beadded.

The adjustment is easily made by reconnecting the quick connect 33 a,opening clamp 28 c and introducing the additional amount of formulatingmedium.

Example 2

With reference to FIG. 4, a suspension of microspheres containing anactive drug substance can be processed in the identical way as thefollowing example performed on blank, polymer only, microspheres.Microspheres were prepared by the process according to theaforementioned co-pending application Ser. No. 08/800,924 filed Feb. 13,1997 U.S. Pat. No. 5,945,126. Aqueous continuous phase, containing 0.35%PVA, from continuous phase tank 112, and dispersed phase comprised of asolution of 14.7% PLGA polymer 503H from Boeringer Ingelheim, 66.2%methylene chloride and 19.1% methanol, from dispersed phase tank 114 wasmetered into a Silverson in-line mixer at a ratio of 80:1 and a rate of2 liters per minute. The impeller in the mixer was run at a rate of 7000rpm to cause the formed or forming microspheres to exit the mixer andenter vessel 316 (Model PTT-75-20-B 20 gallon jacketed 316 L stainlesssteel pressure vessel, Walker Stainless Steel Co) at a rate of 2 litersper minute. In this example, vessel 316 serves as both a solvent removalvessel and a processing vessel for the concentrating and washing steps.

In the previous example, the amount of microsphere suspension that couldbe processed was limited to 40 liters due to the size of the holdingtank 24 (FIG. 2). In this case, the bottom drain of the vessel 316 isconnected to a Watson-Marlow large volume peristaltic pump 340 bysanitary connections (Tri-clover) using silastic tubing (½″ID)). Theoutlet of the peristaltic pump is connected to the bottom fitting of ahollow fiber filter 322 (AIG Technologies Model CFP4-E-55A, 0.45μ). Themicrosphere suspension flows through the hollow fiber filter and isreturned to the vessel 316. After the vessel 316 has filled with 40 L ofmicrosphere suspension, the peristaltic pump 340 is started at a flowrate of 15 liters per minute through the hollow fiber filter 322. Thepermeate flow out of line 332 is adjusted to 2 liters per minute, andthe system is now running at a steady state such that newly formedmicrospheres are entering the vessel 316 at 2 liters per minute, the 40liters of suspension are recirculating through the hollow fiber filterat 15 liters per minute, and 2 liters per minute of microsphere freepermeate are being delivered to a waste container via line 332. In thisexample, the system was utilized to harvest and formulate microspheresdelivered to the system at 2 liters per minute for a total time of onehour and fifty-two minutes. The concentration of the microspheresuspension is about 2.5 g of microspheres per liter, and the totalamount of microspheres formed was 500 g. Thus at the end of the aboveconcentration step, 500 g of microspheres were concentrated from aninitial concentration of about 2.5 g per liter to a final concentrationof 12.5 g per liter.

Removal of excess solvent from the microspheres was accomplished in thesame equipment by continuing above process while adding wash solvent (inthis case water) from wash water source 113 to the system at a rate of 2liters per minute using a peristaltic pump (not shown) and continuing todraw off hollow fiber filter permeate at 2 liters per minute. Thus thevolume and concentration of the microsphere suspension remained constantwhile the solvent concentration of the suspending fluid was reduced froman initial value of 6,360 ppm methylene chloride (determined byheadspace gas chromatography) to a value of 2,618 ppm in twenty minutes.

Residual solvent in the microspheres is not readily removed byprocessing at room temperature. While the solvent in the suspendingmedium was reduced by two thirds during the above washing step, theresidual solvent level in the microspheres themselves was reduced fromabout 80,000 ppm to about 50,000 ppm. Raising the temperature of thesystem is needed in order to reduce the residual solvent level of themicrospheres to acceptably low levels. This is accomplished bycontinuing to deliver wash solvent (now water at 40° C.) at 2 liters perminute and raising the jacket temperature of the holding tank to 40° C.This was accomplished in 30 minutes, and the residual solvent in thesuspending medium was found to be 1,092 ppm. The residual solvent in themicrospheres was 18,000 ppm. This process can be continued until theresidual solvent in the microspheres is reduced to acceptable levels.For the blank microspheres in this example, the residual solvent levelin the microspheres was found to be about 13,000 ppm in 30 minutes ofprocessing at 40° C.; 8,000 ppm in 50 minutes, 5,000 in 85 minutes, andfinally 4,600 ppm in 100 minutes. The process can be continued toachieve still lower levels of residual solvents. In previous trials ofleuprolide acetate, microspheres processed by this technique usingsmaller sized equipment (total amount of microspheres 10 g), residualsolvent levels of less than 71 ppm were achieved. In yet another run ofblank microspheres using the smaller equipment, residual solvent levelsof less than 500 ppm methylene chloride were achieved.

The washed, solvent reduced microspheres in ambient temperature waterwere reduced further in volume by transferring them to a smaller vessel416 and continuing to pump (Watson Marlow 603S) the suspension throughat 5 liters per minute through a second hollow fiber filter 422 (A/GTechnologies, model CFP-4-E-9A,0.45μ), via pump 440, and drawing of fwater at 1 liter per minute, until the total 500 g of microspheres wassuspended in 5 liters of water. The transfer to a second, small vesselwas needed only to minimize the amount of microspheres lost in tubingand the like. Since the internal volume of the large pump, tubing andhollow fiber filter is nearly 2 liters, when the volume is reduced to 5liters the 2 liter potential hold up in the pump and filter cycle of thefirst tank and filter is nearly 40% of the total volume. Thus, tominimize potential losses in the cycle, the suspension is transferred tothe smaller vessel cycle at 416. After the microsphere suspension wasbrought down to a volume of 5 liters, the final formulating medium wasdelivered into the system at 1 liter a minute while fluid was removedthrough the hollow fiber at 1 liter per minute. This was continued for50 minutes, until the microspheres were ready to aseptically fill intovials and freeze dried.

Many modifications and variations of the invention will be apparent tothose skilled in the art in light of the forgoing detailed disclosure.Therefore, within the scope of the appended claims, the invention can bepracticed otherwise than as specifically shown and described.

What is claimed is:
 1. A method of formulating a plurality of activeagent containing polymer bodies comprising: a) providing a suspension ofactive agent containing polymer bodies in a continuous phase in aprocess vessel; b) while maintaining said polymer bodies in suspension,replacing said continuous phase with a formulating medium by moving saidsuspension through a filter adapted to remove continuous phase andreturn said polymer bodies as a suspension to a process vessel; and, c)removing said suspension of active agent containing polymer bodies andformulating medium from said process vessel.
 2. The method of claim 1wherein said filter is a hollow fiber filter.
 3. The method of claim 1or 2 which is aseptic, comprising providing a sterile suspension ofagent containing polymer bodies, replacing said continuous phase withformulating medium and removing said suspension from said process vesselwhile maintaining said polymer bodies sterile.
 4. The method of claim 1further comprising concentrating said suspension of agent containingpolymer bodies in said continuous phase, prior to said replacing step,by moving said suspension through a filter adapted to remove continousphase and return said polymer bodies to a process vessel.
 5. The methodof claim 1 further comprising concentrating said suspension of agentcontaining polymer bodies in said continuous phase to an approximatefinal dosage concentration that is greater than a final dosageconcentration of said polymer bodies per unit volume, prior to saidreplacing step, by moving said suspension through a hollow fiber filter.6. The method of claim 1 further comprising introducing said suspensionof agent containing polymer bodies and formulating medium into finishedproduct containers while maintaining said polymer bodies in suspension.7. The method of claim 1 wherein said agent containing polymer bodiesare microspheres.
 8. The method of claim 1 wherein said agent containingpolymer bodies are microcapsules.
 9. A method of aseptically formulatinga plurality of active agent containing polymer bodies comprising: a)providing a sterile suspension of active agent containing polymer bodiesin a continuous phase in a process vessel; b) washing said active agentcontaining polymer bodies by replacing said continuous phase with waterby moving said suspension through a filter adapted to eliminatecontinuous phase and returning said polymer bodies to a process vesselwhile maintaining said polymer bodies sterile and in suspension; c)while maintaining said polymer bodies sterile and in suspension,replacing said water with a formulating medium by moving said suspensionthrough a filter adapted to remove continuous phase and return saidpolymer bodies to a process vessel; and, d) removing said suspension ofactive agent containing polymer bodies and formulating medium from saidprocess vessel.
 10. The method of claim 9 wherein said step of replacingsaid continuous phase with water is performed by moving said suspensionthrough a hollow fiber filter.
 11. The method of claim 9 wherein saidstep of replacing said water with formulating medium is performed bymoving said suspension through a hollow fiber filter.
 12. The method ofclaim 9 wherein said steps of replacing said continuous phase with waterand replacing said water with formulating medium are performed bycirculating said suspension through the same hollow fiber filter, andreturning said suspension to the same process vessel.
 13. The method ofclaim 9 further comprising concentrating said suspension of agentcontaining polymer bodies in said continuous phase, prior to saidwashing step, by moving said suspension through a hollow fiber filter.14. The method of claim 9 further comprising concentrating saidsuspension of agent containing polymer bodies in said continuous phaseto an approximate final dosage concentration that is greater than afinal dosage concentration of said polymer bodies per unit volume, priorto said washing step, by moving said suspension through a filter adaptedto remove continous phase and return said polymer bodies to a processvessel.
 15. The method of claim 9 comprising moving said suspension fromsaid process vessel to said filter and back to a process vessel whilemaintaining said polymer bodies in suspension whereby losses are nogreater than about 10%.
 16. A method of making and formulating agentcontaining polymer bodies comprising: a) forming a dispersed phasecomprising active agent; b) providing a continuous phase in which saiddispersed phase will form an emulsion, at least one of said dispersedand continuous phases comprising polymer; c) introducing said dispersedand continuous phases into a reactor vessel, said reactor vesselincluding means for forming an emulsion, and forming an emulsion of saiddispersed phase in said continuous phase; d) causing or allowing saidpolymer to form microspheres or microcapsules containing said agent; e)transporting said emulsion from said reactor vessel to a solvent removalvessel and removing solvent therein; f) formulating said polymer bodiesby maintaining a suspension of said polymer bodies in said continuousphase; replacing said continuous phase with a formulating medium bymoving said suspension through a filter adapted to remove continuousphase and return said polymer bodies to a process vessel whilemaintaining said to polymer bodies in suspension; and, removing saidsuspension of agent containing polymer bodies and formulating mediumfrom said process vessel.
 17. The process of claim 16 wherein saidfilter is a hollow fiber filter.
 18. The process of claim 16 whereinsaid solvent removal vessel is different than said process vessel.
 19. Amethod of making and formulating agent containing polymer bodiescomprising: a) forming a dispersed phase comprising active agent; b)providing a continuous phase in which said dispersed phase will form anemulsion, at least one of said dispersed and continuous phasescomprising polymer; c) introducing said dispersed and continuous phasesinto a reactor vessel, said reactor vessel including means for formingan emulsion, and forming an emulsion of said dispersed phase in saidcontinuous phase; d) causing or allowing said polymer to formmicrospheres or microcapsules containing said agent; e) transportingsaid emulsion from said reactor vessel to a solvent removal vessel andremoving solvent therein; f) formulating said polymer bodies bymaintaining a suspension of said polymer bodies in said continuousphase; washing said agent containing polymer bodies by replacing saidcontinuous phase with water by moving said suspension through a filteradapted to remove continuous phase and return said polymer bodies to aprocess vessel while maintaining said suspension; replacing said waterwith a formulating medium by moving said suspension through a filteradapted to eliminate said water and return said polymer bodies to aprocess vessel while maintaining said polymer bodies in suspension; and,removing said suspension of agent containing polymer bodies andformulating medium from said process vessel.
 20. The process of claim 19wherein said steps of replacing said continuous phase with water, andreplacing said water with formulating medium are performed by movingsaid suspension through a hollow fiber filter.
 21. The process of claim19 wherein said solvent removal vessel is different than a processvessel.